It has long been recognized that the two most ultraviolet resistant plastic families are acrylics and fluoropolymers. Both plastics have fairly severe drawbacks when their contemplated end use is as a thin weatherable coating. Fluoropolymers are expensive to make. Physically, they are soft, making them very difficult and expensive to use for most outdoor weatherable coating applications.
Acrylics, on the other hand, are relatively inexpensive. Physically they are hard and brittle.
Both fluoropolymers and acrylics have been used in solvent-borne paint systems where they essentially form small pigmented platelets that are held together by some more suitable backbone resins such as urethanes, latexes, alkyds, etc. While the fluoropolymer and acrylic platelets are ultraviolet resistant, the carrying or backbone resin of the solvent or waterborne coating systems (paint) are not and are, thus, the limiting factor in the serviceable life of these coatings.
Additionally, these systems make extensive use of volatile organic compounds which are regulated as environmental pollutants and are expensive to dispose of. It is also widely known that the weatherability of acrylics increases as the molecular weight of the acrylic increases. However, the melt flow rate (how much flows in a given amount of time at a given temperature and pressure) goes down as molecular weight increases. Thus, the more easily the acrylic is handled (high melt flow), the less optimized it is for weatherability, and also the more brittle it becomes. Thus, the most common weatherable uses of thermoplastic acrylic have been thick sheets of plexiglass having a high molecular weight, such as polymethylmethacrylate (PMMA) (i.e., plexiglass as a thin 2-10 mil calendar rolled film). Normally, these films are calendar rolled with a less brittle, more easily handled, but far less weatherable backing film such as vinyl. For example, high molecular weight PMMA could be nipped between calendaring rolls along with vinyl at temperatures and pressures to form an intimately bonded two layer film 8 mils thick (4 mils each of PMMA and vinyl). In the first instance, the PMMA is so thick, expensive, and hard to conform to a substrate (process unfriendly), it is not typically used as a weatherable coating. In the second instance, the cost of calendar rolling the acrylic/vinyl film itself, and the cost of the application machinery means that, while the material is much more process friendly, it is normally only feasible to use with a specialty, high value product due to high cost per unit of surface area relative to other coating systems.
Various industrially manufactured components are, in use, exposed to the elements. Such elements include rain, snow, wind, temperature extremes, ultraviolet radiation, and chemical pollutants. Further, such components can be, from time to time, exposed to various types of impact.
A typical component of this nature is a window frame or a door frame. Typically, such assemblies are made of wood, vinyl or metal. In order to make them more durable and to overcome some of the limitations caused by the elements discussed above, various types of coatings have been developed and methods for applications of such coverings have been conceived.
A first method of forming a product is known as co-extrusion. In this process, a thermoplastic material such as vinyl is extruded through a forming die to form a profile. Typically, a "capstock", having more expensive pigments, ultraviolet absorbers or blockers, a higher thermoresistance, etc., is concurrently co-extruded to areas that will require greater protection or need a decorative color. Such a "capstock" is a similar thermoplastic material or a compatible thermoplastic.
A second process is known as film wrapping. In this process, a base profile, such as a thermoplastic vinyl extrusion or thermoset pultrusion, is wrapped in a solid, non-molten thermoplastic film. The solid film is, typically, a calendar rolled sheet of two or more plastics (i.e., acrylic and vinyl), and it contains the necessary pigment, ultraviolet absorbers or blockers, etc. The solid film, thereby, provides the protection or decoration to the base profile. In this process, the solid film is secured in place by means of a hot melt or solvent-based adhesive.
A third process known in the art is crosshead extrusion coating or encapsulation. In this process, a profile such as shaped wood is passed through a die which generally conforms to the profile shape. A thermoplastic in flowable form is fed to the die. Typically in this process, the encapsulating material is not required to be adhered to the profile due to the differences in coefficients of thermal expansion. Indeed, it is better if the encapsulating material is not adhered to the profile due to the difference in coefficients of thermal expansion.
None of these methods, however, overcomes the limitations as previously discussed. In some cases, the process proves to be unwieldy; in other cases, the final product does not prove to be sufficiently durable and resistant to ultraviolet radiation, etc. Other drawbacks are cost and time limitations.
It is to these shortcomings and dictates of the prior art that the present invention is directed. It is a process for the manufacture of a reinforced plastic component (for example, of door and window frames) which overcomes many of the deficiencies of the prior art, and a product made in accordance with the process.